The present invention relates to a semiconductor device. More particularly, the invention relates to a semiconductor equipped with an electrostatic capacitance type touch sensor circuit.
In the technical field of touch keys and touch screens, electrostatic capacitance type touch sensor circuits have been widely adopted. U.S. Pat. No. 8,089,289 discloses a structure in which a sigma delta modulation circuit modulates the signal output from a switching capacity circuit into a digital signal. U.S. Pat. No. 7,312,616 discloses a structure in which a comparator compares a reference voltage with the terminal voltage of a device-under-test capacitor charged and discharged repeatedly at a predetermined frequency so that the value of the device-under-test capacitor may be measured. Japanese Unexamined Patent Publication No. 2008-199408 discloses a structure including an oscillation unit of which the frequency varies depending on an operation unit getting touched or not touched so that a frequency change in the frequency signal output from the oscillation unit may be detected.